This invention is directed to cylindrical, rotating thickening device, and, more particularly, to a perforated deck on such a cylindrical rotating thickening device.
During operation, the perforated decking of a press roll must transfer the high loads generated at the nip between rolls and at the roll periphery to the main shell of the roll. Current technology uses shrink fitting or welding of continuous hoops of perforated decking to the shell, to transfer these loads from the cylindrical hoops of perforated deck plate to the main shell of the press roll. Since the cylindrical deck hoops are a continuous ring secured to the roll shell, it is very difficult to replace the deck without removing the roll from the machine. Further, removing such a deck, even when the roll is removed from the machine, is very costly.
Twin roll presses have been used for many years to separate liquids and solids. In the pulp & paper industry, pulp slurry is separated into filtrate and pulp fibers. In the municipal waste industry, sludge is dewatered. In the agricultural and food processing industry, vegetable, fruit and grains are separated into juice and fiber. Twin roll presses consist of two press rolls that are cylindrical in shape and of any diameter and length. The press rolls are typically made of various metals. The surface of the press rolls includes a perforated deck to aid in the pressing and filtering process. In a pulp mill application, the press rolls are horizontally immersed, side-by-side, in pulp slurry contained in a pressurized vat. The rolls are counter rotating with respect to each other. As the periphery of the rolls rotates into the vat, a mat begins to form on the deck plate due to the drainage of the liquid through the perforations in the deck plate. The mat continues to build and liquid continues to drain as it flows from the pressurized vat to the atmospheric channels inside the roll. The roll and pulp mat continue rotating to a nip formed by the two rolls where the pulp mat is squeezed to remove more of the remaining liquid. The dewatered pulp fibers are then doctored off the rolls and transferred out of the press vat by a conveyor.
Typically, the press rolls include an axial core upon which there is an array of longitudinal extending spaced apart support ribs. These longitudinal ribs support a shell at the outer edges of the ribs. There are several designs of shells at this time. Typical shells are either of a heavy walled hollow cylinder with circumferential grooves, with radial holes, and lands, or of a series of individual ribs spaced apart to form spaces and lands. In both types of shell, it is the lands or ribs that support the perforated deck, and the grooves with holes or the spaces between the ribs, allow for the passage of the liquid to the interior of the press roll where it is then drained away.